Mixing process and extrusion of solid propellants

ABSTRACT

An improved extrudable, high energy solid propellant composition consisting essentially of the copolymer of vinylidene fluoride and perfluoropropylene (Viton), an inorganic oxidizer such as ammonium perchlorate, potassium perchlorate or ammonium nitrate, and a metal powder such as aluminum, beryllium, magnesium or zirconium. This composition is extrudable into any suitable shape and has a very high percentage theoretical maximum density so as to be practical for utilization in rocket motors for propulsion.

United States Patent 1 1 Kaufman MIXING PROCESS AND EXTRUSION v0F SOLID PROPELLANTS Inventor: Martin H. Kaufman, China Lake,

Calif.

Assignee: The United .States of America as represented by the Secretary of the Navy Filed: June 11, 1968 Appl. No.: 738,721

Related U.S. Application Data Continuation of Ser. No. 361,612, April 17, 1964.

U.S. Cl. ..264/3 B, 149/22, 149/40, 149/41, 149/42, 149/43, 149/44 Int. Cl. ..'.....C06b 21/02 Field of Search ..264/3; 149/22, 60, 40, 42, 149/43, 44, 41, 76, 85,19, 20

[56] References Cited UNITED STATES PATENTS 3,155,749 11/1964 Rossen et al. ..264/3 3,351,505 11/1967 Shapiro et a1. 3,431,154 3/1969 Kelly et al ..149/44 X Primary Examiner-Stephen J. Lechert, Jr. Attorney-George J. Rubens and Roy Miller [57] ABSTRACT An improved extrudable, high energy solid propellant composition consisting essentially of the copolymer of vinylidene fluoride and perfluoropropylene (Viton), an inorganic oxidizer such as ammonium perchlorate, potassium perchlorate or ammonium nitrate, and a metal powder such as aluminum, beryllium, magnesium or zirconium. This composition is extrudable into any suitable shape and has a very high percentage theoretical maximum density so as to be practical for utilization in rocket motors for propulsion.

4 Claims, No Drawings MIXING PROCESS AND EXTRUSION OF SOLID PROPELLANTS REFERENCE TO RELATED APPLICATION This invention is a continuation of US. Pat. application Ser. No. 361,612, filed in the U. S. Patent Office on 17 April 1964.

BACKGROUND OF THE INVENTION The present invention relates to an improved extrudable, high energy, high density solid propellant and to the method of preparation thereof.

Those concerned with the development of solid propellants have long known and recognized the need for a propellant with a high delivered density-impulse, high temperature stability and good safety characteristics. A propellant of this kind finds greatest use in the system where the propellant burnout mass is very large compared to the propellant volume. As variations in the properties are required for a specific application, variations in the formulation are needed. Propellants presently available have density specific impulse values on the order of 430 470 g-sec/cc. The achievement of high density in a composite propellant is controlled by the density and generally the particle size of the ingredients and ultimately the method of fabrication which is limited often by safety features of the processing system. Harsh working of the material may cause ignition.

The present invention attains a very high theoretical density impulse of a value between 490 and 622 gsec/cc which is a considerable increase over prior propellant compositions. Physical properties are I changed; for instance, tensile strength is increased.

Burning rate modifiers can be added to a basic composition in order to improve ballistic properties of the composition. The general purpose of this invention, therefore, is to produce a basic family of dense propellants which are extrudable or can be compression molded and which have suitable impulses that increased range results from their use in volume limited boost type application.

SUMMARY OF THE INVENTION The present invention is for an extrudable, high density solid propellant composition and its method of preparation. The composition consists essentially of a fluorocarbon binder, such as a copolymer of vinylidene fluoride and perfluoropropene (Viton) or a copolymer of vinylidene fluoride and trifluorochloroethylene (Kel-F elastomer), in the range of from to 35 percent; elemental fuels and their hydrides or mixtures thereof, selected from the group consisting of aluminum, boron, zirconium, beryllium, titanium, magand metal powder thereby forming a suspension. The suspension is then washed with a quantity of a precipitant for the fluorocarbon, in this instance hexane. The solid is permitted to settle and the liquid is decanted off. The solid is washed again with hexane after which the liquid is decanted off, the solid filtered and air dried or oven dried. The powder resulting is compression molded or extruded into the desired shape. The object of this method to produce an extrudable, high density solid propellant material which will have greater boost velocity than existing propellants. A product which is relatively safe to handle is formed and the process is amenable to large scale production of propellants, pyrotechnics, and explosive materials such as high energy, high density molding powders which can be molded or extruded.

Other objects and many attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying graphs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the theoretical impulse as a function of the basic composition;

FIG. 2 is a graph showing the theoretical impulse as a function of a zirconium modified basic composition;

FIG. 3 is another graph showing the theoretical impulse as a fimction of a beryllium modified composition;

FIG. 4 is yet another graph showing the theoretical impulse as a function of another modified basic composition; and

FIG. 5 is a graphic comparison of the boost velocities of fluorocarbon bound propellants with propellants containing conventional binders.

DESCRIPTION OF THE INVENTION In the present invention many compositions were studied, extruded, or pressed and fired. This invention is illustrated, but not limited, by the following basic composition consisting essentially of a fluorocarbon binder, such as a copolymer of vinylidene fluoride and perfluoropropene (Viton) and a copolymer of vinylidene fluoride and trifluorochloroethylene (Kel-F elastomer), in the range of from 10 to 35 percent; elemental fuels and their hydrides or mixtures thereof, such as aluminum, boron, zirconium, beryllium, titanium, magnesium, and their hydrides, in the range of from about 5 to percent; and an oxidizer, generally an inorganic oxidizer such as ammonium or alkali metal perchlorate in the range of from about 25 to percent.

In the use of very dense metals, less binder is required on a weight basis as the fuel volumes get smaller. For example, the density of boron is 2.34 g/cc, but the density of lead is 11.4 g/cc, and that of tungsten is 19.32 glcc.

Oxidizers such as ammonium or alkali perchlorates and nitrates are interchangeable as far as processing is concerned. Calculations indicate that oxidizers such as hydrazine nitroformate will theoretically provide even better performance.

The following basic composition was modified as hereinafter described.

Basic Composition Constituents Percent by weight Ammonium perchlorate 59 Aluminum 21 Viton A 20 The addition of various fuel mixtures to the above extrudable basic composition provided changes in burning rates which are shown in the-following table. For example, the addition of copper, iron, boron, chromium, zirconium, or their derivatives at the percent level in the basic composition showed significant burning rate changes:

TABLE I Burning Rate (in/sec.)

1000 psi 4000 psi Basic fonnulation 0.47 1.07

Extruded basic formulation modified by addition of Ferrocene 0.70 1.5 Copper 0.54 1.1 Boron 0.72 1.65 Chromium 0.5 1.1 Copper Chromite 0.64 1.5 Copper Stearate 0.56 1.2 Copper Oxide 0.56 1.2 Lead Salicylate 0.52 1.0 Lead Resorcylate 1.10 Titanium Dioxide 0.58 1.37 Zirconium Boride 0.53 1.35 Lead Carbonate 0.52 1.35

Mixtures of aluminum and zirconium as high energy, high density ingredients also produced significant changes in the burning rate of the extruded basic composition as shown in the following table:

TABLE 11 Burning Rate (in/sec.)

Composition Burning Rate (Percent by Weight) (psi) Viton AN Al KP Zr Tef IOOOAP 4000 15 45 20 15 5 0.60 1.35 15 45 20 20 0.77 1.95 30 20 50 0.47 1.22 20 80 0.40 0.82 25 75 0.40 0.84 15 85 0.06 0.15 15 75 0.45 0.92 16 50 20 10 4 0.63 1.35 18.5 45 16.5 16.5 3.5 0.53 1.25

AP ammonium perchlorate AN ammonium nitrate A1 aluminum KP potassium perchlorate Zr zirconium Other modifications of the basic composition which showed significant changes in the burning are as follows:

Modified Composition A Constituents Percent by weight Viton l 8.5 Sodium azide 9.1 Ammonium perchlorate 54.6 Aluminum 1 8. l 5

The sodium azide acts as a catalyst. Burn rate results of the extruded strands were as follows:

0.37 in/sec at 1000 psi 0.78 in/sec at 4000 psi Modified Composition B Constituents Percent by weight Viton 25 Magnesium 20 Ammonium perchlorate Burn rate results of the extruded propellant were as follows:

0.54 in/sec at 1000 psi 1.07 in/sec at 4000 psi The process by which the present invention is made uses a resin kettle with a fast propeller stirrer and a stiff rubber baffling device to prevent vortex formation. A stainless steel drum may be used to make larger batches. The required quantity of binder is placed in a container and dissolved in acetone or other suitable solvents such as methylethyl ketone and ethyl acetate. Approximately 25 cc of acetone per gram of Viton or Kel-F elastomer is used. Into this solution at room temperature are stirred the dry solid ingredients, the metal powder and oxidizer. After about 5 minutes of stirring the suspension a quantity of a precipitant for the fluorocarbon, about two and one-half times by volume that of fluorocarbon solvent is added with stirring. l-lexane was used in this instance. Other hydrocarbons such as petroleum ether may be used. After an additional 5 minutes of stirring, the solid is permitted to settle and the liquid is decanted off. Care must be taken at this point to prevent complete decantation, especially prior to the first washing. Residual solvent will permit easy agglomeration of the powder at this stage if most of the hydrocarbon evaporates off. The latter is detrimental to the preparation of a free-flowing molding powder which is suitable for extrusion. The remaining wet solid receives a second hexane wash after which it is decanted off, filtered and air dried or oven dried at C. In this manner agglomeration is avoided. If a finer powder is desired, the second hexane wash may be decanted off and the wet solid screened. The powder after air drying and vacuum drying is compression molded or extruded into the desired shapes. The propellant surfaces not to be burned are inhibited prior to motor firmg.

Referring now to the drawings, FIG. 1 is a graphic view of the theoretical specific impulse as a function of the basic formulation, as above set out, consisting essentially of Viton, aluminum, and ammonium perchlorate. FIG. 2 illustrates the theoretical specific impulse as a function of the composition wherein the basic formulation was modified by using zirconium as the elemental fuel in place of aluminum. In FIG. 3 the theoretical specific impulse as a function of the composition is shown in which beryllium was the elemental fuel used. FIG. 4 illustrates the theoretical impulse as a function of the composition wherein hydrazine nitroformate is the oxidizer with a fluorocarbon binder and the fuel, beryllium. FIG. 5 compares the boost velocities of fluorocarbon bound propellants with propellants bound with conventional binders such as polyurethanes and polyhydrocarbons. These conventional binders are designated by the symbol Cl-l The performance of an ideal rocket, i.e., no pressure thrust, drag or gravitation or what may be termed a gravitationless vacuum is given by The logarithmic relation makes V very dependent on a mass ratio. If the rocket were all propellant the V would theoretically be infinite. Now if m (mass of rocket at burnout) m, m,, and since,

m, density of propellant, p, x volume of propellant,

so that BO 8Dg [Pp 50/ vl) wherein V Velocity of rocket at propellant burnout C,,,, Time average exhaust velocity (cm/sec) 1,,

m, Total rocket mass at time zero m, Total propellant mass at time zero t Time I Specific impulse g =Gravity Since the mass of a rocket without propellant, and the volume to be occupied by the propellant generally are both fixed by design, the ratio "130/ V, (very often called the mass to volume ratio) is independent of propellant characteristics and actually characterizes the rocket or missile.

In FIG. it is shown that the boost velocity (V of fluorocarbon bound propellant is considerably better than the conventional binders.

The following table shows test results of several batches of propellants prepared in accordance with the present invention.

Y IKEIZE 1 11 Composition (percent Meas- Percent by weight) Composition ured theoretical Measby analysis, denmaximum ured Viton AP Al Zr V/AP/Al/Zr sity density 1.,

V Viton The invention described herein may be manufac- 5 tured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

l. The process for preparing an extrudable, high energy solid propellant comprising the steps of l. dissolving a copolymer of vinylidene fluoride and perfiuoropropylene in acetone to form a solution;

2. adding while stirring weighed quantities of a dry oxidizer selected from the group consisting of ammonium perchlorate, ammonium nitrate, potassium perchlorate and mixtures thereof and a fuel selected from the group consisting of aluminum, boron, beryllium, magnesium, and zirconium to form a homogeneous mixture;

3. adding to said mixture while stirring a volume of hexane about three times the volume of said acetone; permitting said acetone and mixture to stan without stirring until all the solids settle;

5. decanting off substantially all the liquid leaving a residue;

6. washing the residue with hexane of about three times the volume of acetone;

7. filtering out said residue;

8. air drying the residue; and

9. extruding said residue.

2. The process as defined in claim 1 wherein the oxidizer is ammonium perchlorate and the fuel is aluminum.

3. The process as defined in claim 1 wherein the oxidizer is ammonium perchlorate and the fuel is zirconi- 4. The process as defined in claim 1 wherein the oxidizer is ammonium perchlorate and the fuel is berylli- 

2. adding while stirring weighed quantities of a dry oxidizer selected from the group cOnsisting of ammonium perchlorate, ammonium nitrate, potassium perchlorate and mixtures thereof and a fuel selected from the group consisting of aluminum, boron, beryllium, magnesium, and zirconium to form a homogeneous mixture;
 2. The process as defined in claim 1 wherein the oxidizer is ammonium perchlorate and the fuel is aluminum.
 3. The process as defined in claim 1 wherein the oxidizer is ammonium perchlorate and the fuel is zirconium.
 3. adding to said mixture while stirring a volume of hexane about three times the volume of said acetone;
 4. permitting said acetone and mixture to stand without stirring until all the solids settle;
 4. The process as defined in claim 1 wherein the oxidizer is ammonium perchlorate and the fuel is beryllium.
 5. decanting off substantially all the liquid leaving a residue;
 6. washing the residue with hexane of about three times the volume of acetone;
 7. filtering out said residue;
 8. air drying the residue; and
 9. extruding said residue. 